1. Field of the Invention
The present invention concerns a method for forming a common transfer contact on a thin film transistor (TFT) liquid crystal display (LCD) and the resulting apparatus, wherein a common transfer contact serves to connect an electrode disposed on a common electrode substrate to another electrode arranged on a TFT substrate.
2. Description of the Related Art
A TFT LCD typically includes pixels each connected to a TFT transistor formed of amorphous silicon coated on a glass substrate. The liquid crystals are twisted nematic (TN). In such a TFT LCD, each pixel is turned on only when receiving an electrical signal, to avoid cross talk phenomena. Additionally, each pixel is connected with an electrical capacitance formed by the thin film, which stores electrical charges to keep a display image even during a non-selection period.
The processing steps of fabricating the TFT LCD includes:
1. Preparing a TFT substrate PA1 2. Preparing a common electrode substrate PA1 3. Assembling the substrates together PA1 4. Filling liquid crystals PA1 5. Testing PA1 6. Fabricating a module
For the TFT LCD to operate properly, an electrical transfer contact must be provided between the TFT and the common electrode substrates. This electrical transfer contact serves to connect an electrode disposed on the common electrode substrate to another electrode arranged on the TFT substrate. A conventional method of forming the transfer contact of the TFT LCD will now be described with reference to FIGS. 1 to 6.
A common electrode substrate 1 with an alignment layer is printed with a seal pattern 3 of a proper sealant such as thermosetting resin by employing a screen mask, as shown in FIG. 1. The seal pattern 3 is to seal the inside between the common electrode substrate 1 and the TFT transistor substrate 2 assembled with a proper gap. After printing the seal pattern 3, a conductive material such as Ag is dotted to form a transfer contact 4 along the outside of the seal pattern 4.
Thereafter, the common electrode substrate 1 and the TFT substrate 2 are pressed together with heat facing each other, so that the seal pattern 3 and the transfer contact 4 are hardened to sealingly assemble the two substrates with a proper cell gap maintained by the spacers (not shown) interposed between the two substrates, as shown in FIG. 3. Cutting the common electrode substrate 1 along a cutting line 6 as shown in FIG. 4, the cross section of the assembled LCD has a structure as shown in FIG. 5.
Such method of forming the transfer contact increases the seal region L1 occupied by the seal pattern 3 and the transfer contact 4, as shown in FIG. 6, so that the effective display region 5 is reduced compared to the seal region.
Another conventional structure of the common transfer contact is disclosed in U.S. Pat. No. 4,469,410 entitled "Common Transfer Contact for Liquid Crystal Display Cell or Electrochromic Display Cell" granted on Sep. 4, 1984, where the common transfer contact 4 is encircled by a seal material 3 when sealingly assembling the TFT substrate 2 and the common electrode substrate 1, as shown in FIG. 7. This structure also cannot help but decrease the effective display region compared to the seal region.